In thick walled metal conduit, especially two inches in diameter and above, threads are often provided on the ends of the conduit units or sections which come in lengths from 10 to 20 feet. Threads on the ends of the conduit units enable them to be joined together end-to-end or to other components, such as elbows and electrical boxes, in electrical systems.
Particularly in metal conduits of sizes 2 inches and larger it is difficult to manipulate the conduit units and align them for end-to-end connections or for connection to other components, such as elbows or the like, in an electrical system. Moreover if a conventional union, a sleeve which has internal threads, is used to connect the threaded ends, the conduit units must be rotated relative to one another to screw them into the union. In some situations it is not possible to rotate conduit units relative to other components in the system.
Further if unions are used, it difficult to disassemble such an electrical system for upgrade and or repair as the conduits must be unscrewed.
Due to the above difficulties, it has become common practice to use what is known in the trade as a three piece coupling to join the threaded ends of a conduit unit with other conduit units end-to-end or to other threaded components in an electrical system. These fittings have a threaded bushing, with internal and external threads, which is screwed onto a threaded end of one of the conduit units. The second element is a sleeve which slips onto the end of the other conduit unit, after which the third element, a threaded collar, is screwed on the end of this conduit unit. The bore in the sleeve is large enough to allow the sleeve to pass over the collar but includes a rim at its opposite end that engages this collar preventing it from passing through the sleeve. As the end of the sleeve which passes over the collar includes internal threads, it can be advanced and screwed onto the external threads of the threaded bushing by rotating the sleeve without rotating either conduit unit. As the sleeve advances on the threaded bushing its rim will engage the collar and pull the ends of the conduit units together.
Such three piece units, described in National Electrical Code Handbook which is published every three years, develop a satisfactory mechanical joint and enable assembly in confined spaces, which accounts for the broad use in the filed. There are variation in the design of such units, such as those illustrated in U.S. Pat. No. 4,258,936 issued to Goldberg, U.S. Pat. No. 4,549,765 issued to Basile and U.S. Pat. No. 4,592,574 issued to Vollmuth et al, all of which devices use a sleeve associated with one of the conduit units which is rotated to screw it onto the threads of a bushing on the other conduit unit without rotating either of the conduit units. U.S. Pat. No. 4,957,413 issued to Basile, et al, teaches a two piece coupling unit that has set screws engaging a groove to lock the elements screwed onto the conduit units together, which is generally not commercially available because there is no way to mechanically pull the conduit units together so the set screws can be properly engaged in the groove, with the exception of smaller conduit installations, i.e., employing conduits one inch or less in diameter.
In the above referenced handbook the specification for couplings, such as the three piece coupling, in Section 848-7 are
xe2x80x9cCouplings and Connectors. Couplings and connectors used with tubing shall be made up tight. Where buried in masonry or concrete they shall be concrete tight. Where installed in wet locations they shall be the raintight type.xe2x80x9d
Applicant, an electrical contractor, has tested the commercially available three piece couplings for larger size conduits by closing off one end or a short piece of conduit and joining another piece of conduit to it with such couplings. Thereafter, when submerging the short piece of conduit and coupling in a pail of water, the joint leaked and the conduit filled with water.
In part, water ingress results from variations in the outside diameter of the conduits and variations in the inside diameter of the couplings, which in larger conduit size installations can result in gaps in the range of 0.060 inch (or more) between the conduit and the coupling parts. Moreover the three piece couplings must have enough tolerance to allow the unit to be used, requiring a somewhat sloppy fit between its components because conduit units do not perfectly align with one another in the field. In addition these couplings, even when aggressively tightened cannot bring the ends of the conduit units in to a sealing contact with each other due to variations in the ends of the conduit units, alignment, etc.
On the roofs on commercial buildings, exterior walls and in industrial plants threaded conduit units are installed with three piece couplings which are not raintight even though the specifications for these installations, more often than not, require that the threaded couplings be xe2x80x9clistedxe2x80x9d as raintight.
While rain water is essentially distilled water with few impurities, once it contacts a metal conduit it dissolves metal atoms, along with other impurities, and becomes conductive when it enters the interior of such conduits through a coupling which is not raintight. As such water passes through the interior of the conduit system it dissolves impurities and may short out electrical circuits, switch gear and the like. Of course corrosion from the intrusion of the rain water compromises such installations still further.
An object of the current invention is to provide an improved three piece coupling which is raintight and can be used in wet locations, including being buried in the ground where it is likely to be in contact with ground water.
Another object is the provision of a three piece coupling that is raintight and insures electrical continuity through the coupling.
Still a further object is the provision of a raintight three piece coupling which is economical to manufacture and competitive with existing non-raintight couplings of this type.
A water tight three piece coupling for joining threaded components, such as electrical conduits, without the need to rotate such components relative to each other, includes (1) a bushing having internal threads for assembly with the threaded end of a conduit and external threads along with a boss having a diameter larger than its external threads formed on the bushing, (2) a sealing member disposed with the boss, (3) a sleeve having internal threads at one end operable to mate with said external threads of the bushing whereby sleeve can be screwed on to the bushing and a lip on the sleeve which extends beyond its internal threads and operable to engage the sealing member on said boss to effect a seal between sleeve and the bushing, (3) a collar having internal threads sized to fit within the sleeve without restricting rotation of the sleeve, the collar engaging an internal end of said sleeve without the internal threads whereby the collar is advanced with the sleeve and (4) sealing means associated with end of the sleeve without the internal threads operable to seal the sleeve to a conduit connected to the collar through its internal threads in the coupling.